Electronic devices use radio-frequency (RF) signals to communicate information. These radio-frequency signals enable users to talk with friends, download information, share pictures, remotely control household devices, receive global positioning information, employ radar for detection and tracking, or listen to radio stations. As a distance over which these radio-frequency signals travel increases, it becomes increasingly challenging to distinguish the radio-frequency signals from background noise. To address this issue, electronic devices use low-noise amplifiers (LNAs), which amplify a radio-frequency signal without introducing significant additional noise. Performance of a low-noise amplifier depends on several factors, including impedance matching and linearity.
As electronic devices communicate over different distances, desired amounts of amplification by the low-noise amplifier can vary. Consider a mobile phone communicating with a base station. If the mobile phone is far from the base station, a strength of the radio-frequency signal may be low; thus, it may be desirable for the low-noise amplifier to provide more amplification. In contrast, if the mobile phone is close to the base station, the strength of the radio-frequency signal may be high; thus, it may be desirable for the low-noise amplifier to provide less amplification. It becomes challenging, however, to design a low-noise amplifier to support different amounts of amplification, which are referred to as different gain modes.